Field of the Invention
The present invention relates to a stereoscopic image display device and, more particularly, to a switchable 3-dimensional conversion device having a spacer stably formed at a predetermined height by imprinting, a manufacturing method thereof and a stereoscopic image display device having the same.
Discussion of the Related Art
Services for rapidly providing information over a high speed communication network have been developed from ‘listening and speaking’ services, such as provided by a telephone, to ‘viewing and listening’ multimedia type services using a digital terminal for rapidly processing text, voice and image data and, ultimately, to a three-dimensional stereoscopic information communication service for providing realistic stereoscopic viewing and entertainment, in order to ‘3-dimensionally viewing and enjoying above time and space’.
In general, the eyes form a three dimensional image based upon the principle of stereovision. Since two eyes have a disparity therebetween, that is, since two eyes are separated from each other by about 65 mm, the left eye and the right eye view slightly different images. A difference between images caused by such difference between the positions of the two eyes is referred to as ‘binocular disparity’. A three-dimensional image display device enables the left eye to view only an image for the left eye and the right eye to view only an image for the right eye according to such binocular disparity.
That is, the left and right eyes view two different two-dimensional images. Once these images are received by the retina and sent to the brain, they are processed into a three dimensional image by the brain, providing a sense of depth to the viewer. This capability is generally referred to as ‘stereography’ and a device having this capability is referred to as a stereoscopic image display device.
Meanwhile, stereoscopic display devices may be classified according to the components used to implement 3-dimensional (3D) display. For instance, a device using a liquid crystal layer, which can alter the path of light and induce a different in light path in a manner substantially equal to that of a lens, is referred to as an electrically-driven liquid crystal lens type device.
In general, a liquid crystal display device includes two opposing electrodes with a liquid crystal layer interposed therebetween. Applying voltage to the foregoing electrodes may generate an electric field to drive liquid crystal molecules in the liquid crystal layer. The liquid crystal molecules have polarity and optical anisotropy. Polarity means that the liquid crystal molecules have different charges, which move to respective ends thereof and are oriented in specific directions (polarized) when placed in an electric field, thereby allowing modification in molecular arrangement depending upon an applied electric field. On the other hand, optical anisotropy means that a path of light or polarization thereof is varied depending upon angle of incidence of light or polarization of the same, on the basis of an elongated and narrow structure of a liquid crystal molecule as well as the foregoing orientation for molecular arrangement.
As a result, the liquid crystal layer has a difference in transmittance due to voltage applied to two electrodes and may display images by altering the difference in respects to pixels.
In recent years, an electrically-driven liquid crystal lens having a liquid crystal layer functioning as a lens based on characteristics of liquid crystal molecules has been proposed.
Specifically, the lens utilizes a difference in refractive indexes between a lens material and air to control an incident light path per location basis on the lens. Applying different voltages to the liquid crystal layer depending upon different parts of electrodes in order to form an electric field, the liquid crystal layer may be driven and the incident light entering into the liquid crystal layer may sense phase changes on different sites of incidence to the liquid crystal layer. As a result, the liquid crystal layer may control the path of the incident light, like an actual lens.
The following description will be given to explain an electrically-driven liquid crystal lens typically used in the art.
FIG. 1 is a cross-sectional view illustrating an electrically-driven crystal lens of related art, and FIG. 2 is a schematic view illustrating a lens formed by the electrically-driven liquid crystal lens of related art.
Referring to FIG. 1, the electrically-driven liquid crystal lens of related art consists of first and second substrates 10 and 20 arranged opposite to each other, and a liquid crystal layer 30 interposed between the first and second substrates 10 and 20.
In this case, the first substrate 10 has first electrodes 11 at a first interval and a distance between adjacent first electrodes 11 is referred to as ‘pitch.’ The first electrodes are formed by repeating the same patterns at a cycle of the pitch.
The second substrate 20, provided opposite the first substrate 10, may have a second electrode 21 throughout an inner surface thereof.
Here, since liquid crystal molecules in the liquid crystal layer 30 act on the basis of the strength and distribution of the electric field, the molecules follow a parabolic potential profile thus having a phase distribution similar to an electrically-driven liquid crystal lens shown in FIG. 2.
In order to maintain a predetermined gap between the first and second substrates 10 and 20, ball spacers 40 are provided. The ball spacers 40 are randomly dispersed on either of the substrates and freely move about the surface of the substrate, that is, are not fixed to a given position.
Such an electrically-driven liquid crystal lens of related art is fabricated under specific conditions in that high voltage is applied to the first electrode 11 and the second electrode 12 is grounded. These voltage conditions cause the electric field strength to peak at the center of the first electrode 11 while decreasing with increasing distance from the first electrode 11. Accordingly, when the liquid crystal molecules forming the liquid crystal layer 30 have positive dielectric anisotropy, these molecules are arranged along the vertical field, which in turn stand upright at the center of the first electrode 11 while being inclined toward a horizontal line with increasing distance from the first electrode.
Therefore, in view of light transmission as shown in FIG. 2, the light path is short at the center of the first electrode 11 and is extended with increasing distance from the first electrode 11. Illustrating this condition based upon phase patterns, light transmission effects similar to a lens having a parabolic surface may be obtained.
In this regard, the first electrode 11 and the second electrode 21 cause behavior of a liquid crystal electric field and induce a light refractive index to meet a parabolic spatial function mode. The first electrode 11 also corresponds to a corner part (edge area) of the lens.
Here, since the first electrode 11 receives a slightly higher voltage than that applied to the second electrode 21, a potential difference is generated between the first and second electrodes 11 and 21 as shown in FIG. 2, thus causing a sharply inclined field on the first electrode 11. Therefore, the liquid crystal does not have a smooth distribution but is slightly distorted, thus not having a parabolic type refractive index distribution or being very sensitive to applied voltage.
An electrically-driven liquid crystal lens of related art as described above has the following problems.
An electrically-driven liquid crystal lens of related art may be formed by forming liquid crystals and electrodes on both substrates arranged at opposite sides of the liquid crystals and applying voltage to the electrodes, eliminating the need for a lens having a parabolic surface.
In order to stably maintain a cell gap of a liquid crystal layer placed between both the substrates, ball spacers are dispersed therebetween. However, the liquid crystals do not act at specific positions where these spacers are present, thus neither embodying lens effects nor displaying images due to being obscured by the ball spacers. Otherwise, the ball spacers may induce light scattering, in turn generating crosstalk in the 3D display.
In addition, other problems including, for example, reflection at sites where the ball spacers are present, faults such as rain effects caused when the ball spacers move in the liquid crystal field lens due to fluidity (that is, mobility) of the ball spacers, or the like, may be encountered.
Moreover, when the cell gap is increased to increase a height of the electrically-driven liquid crystal lens, each ball spacer must have a correspondingly large diameter. However, an increase in the diameter of the ball spacer may result in an increase in overall volume of the ball spacer. As a result, not only top and bottom areas but also left and right areas hidden by the ball spacer may be enlarged. Briefly, if the ball spacer has increased diameter, an area of the lens hidden by the ball spacer may be increased, thus reducing an aperture ratio. Furthermore, there is a need for novel materials to fabricate a ball spacer with increased diameter.